1. Field of the Invention
The present invention relates to eye tracking systems generally and, more particularly, but not by way of limitation, to novel eye tracking system with a larger field of view and a higher resolution imager.
2. Background Art
While the present invention is described generally in the context of determining inattentiveness of the driver of a vehicle, it will be understood that the invention is application, as well, to any situation in which tracking of eye movements is desirable.
Communities in which eye tracking is used include the medical, research, and academic communities where eye tracking is useful, for example, in determining psychological response and how a person scans.
A large number of the approximately 35,000 vehicular deaths and a much larger number of vehicular accidents each year in the United States can be attributed to driver inattention. Driver inattention may result from drowsiness, use of a telephone, use of a computer, changing stations on a radio, conversing with another occupant of the vehicle, and similar causes. Whatever the cause, such driver inattention may result in fatalities and non-fatal accidents.
In response to this problem, systems have been developed to continuously track an eye of a driver and use this information to determine when the driver becomes inattentive and to institute measures to alert the driver of the potential disaster. Eye tracking can be an accurate, non-intrusive, non-contact method, which detects driver inattention and fatigue by recording eye movement. Parameters such as blink duration, blink frequency, and eye closure can be useful for detecting drowsiness, fatigue, and other causes of inattentiveness. Pupillary data such as diameter, shape, location, and rate of change can be useful in determining the direction of the driver's gaze and workload. Thus, it is a key safety system that can be used to determine the state of the driver for workload management systems.
Although there are a number of eye tracking methods, many are quite expensive and many involve undesirable intrusiveness, both undesirable features for a vehicular system. Some of these methods are discussed below.
The limbus eye tracking method utilizes the difference in reflectance between the sclera and the iris. The reflectively difference produces a contrast that can be monitored by photodetectors mounted on either side of the eyeball. This method requires head mounted sensors and, when used alone, is sensitive to head movement when calculating gaze.
The pupil tracking method is similar to the limbus tracking method, except that it uses the boundary between the pupil and iris, rather than the boundary between the sclera and the iris. This method is advantageous in that the pupil is far less covered by the eyelid than is the limbus and the border is sharper than that of the limbus, thus offering a higher resolution. A disadvantage is that the contrast is lower.
The cornea/pupil relationship method may be one of two types. In dark pupil tracking, collimated, on-axis IR illumination causes a dark pupil to appear bright. The high contrast with the dark pupil acts as a light sink. In bright pupil tracking, uncollimated, off-axis IR illumination reflects off the retina similar to the reflection seen from the eyes of a nocturnal animal or in red-eye from flash photography. In either case, a CCD or CMOS detector is used, Pupil edge is located and the center is calculated.
The artificial neural network method uses brain waves and artificial intelligence in software to calculate alertness, etc. Capturing the brain waves requires the use of electrodes placed on the scalp or placing the subject in an MRI type of device
The dual Purkinje image method compares the corneal reflection to the reflection from the back surface of the lens. Measurements are made of the relative displacement between the first and fourth reflections, to the shape and size of the pupil, which represent the focal point. Because the IR illumination has to travel through seven interfaces, the method is very inefficient and requires a relatively powerful illumination source.
The electro-oculographic method calculates eye position by measuring the potential difference between the front and back of the eyeball. This method is simple, but not reliable, due to signal variations over time, and not precise, due to noise levels. Of course, electrodes must be placed around the eye.
The search coil method requires that induction coils be embedded in the sclera or in tight fitting contact lenses. This is a very accurate method, but also quite intrusive.
The video-oculographic method gives an accurate measurement of eye components, including ocular torsion. The method also provides pupil diameter measurement and monocular and binocular measurement with pupil diameter. There is no drift and reduced noise sensitivity.
As noted above, the foregoing methods are unsuitable for vehicular use because of cost and/or intrusiveness, although some produce fairly accurate results.
Commonly, a system used in vehicular eye tracking includes one or two IR sources directed at an eye of the driver, a combination of mirrors and motors, an eye camera module, and a processing and control unit. As the two light sources shine on an eye, two spots (invisible, but seen by the infrared camera) occur in the pupil. The eye camera module captures and sends an image of the eye to the processing and control unit, which calculates the direction of driver gaze by comparing the locations of the two spots in the pupil. The mirror/motor combination is used in front of the eye camera adjusts to try to track the driver's eye as the driver's head is moved and also adjusts to driver height through calibration. This requires a complex and expensive auto focus and tracking system.
One problem is that such current eye tracking systems use a small field of view lens to cover a small area around the eye of the driver and an image sensor having a sub-QVGA (“quarter video graphic array) resolution (or one-quarter of the standard 640×480 VGA pixelation). Because of these limitations, conventional eye tracking systems permit only limited head movement. If the limited degree of head movement is exceeded by sudden head movement, head rotation, or vibration, for example if the vehicle runs on a rocky road, the system will “lose” the eye and becomes ineffective until the eye can again be tracked which can take some time.
Another problem with such current eye tracking systems is that, since each person has a slightly different ocular profile that can result in a large error in calculation, the eye tracking system needs to be calibrated for each different driver. This is done by having the driver sit still in the driver's seat, while an instructor sits in the front passenger seat. The instructor tells the driver to look at a particular spot, or fixate on predetermined alignment coordinates, for a short period of time. The instructor then measures and records oculometric data. This procedure is repeated some six or nine times. Then, the instructor takes the recorded data and develops an ocular profile of the driver that is recorded in a look-up table that is manually accessed for each driver. This must be done for each potential driver of the vehicle. In addition to the fairly tedious start-up procedure, periodic recalibration is required because of drift.
In addition to the above problems, the use of electromechanical components inherently renders a system complex and relatively costly and introduces additional areas in which alignment is critical and in which the wearing of mechanical linkages eventually introduces additional errors into the eye tracking system. Accordingly, it is a principal object of the present invention to provide an eye tracking system that has no mechanical linkages.
It is a further object of the invention to provide such an eye tracking system that can increase the field of view to well beyond the area around the eye, while maintaining adequate resolution.
It is an additional object of the invention to provide such an eye tracking system that is automatically calibrated for each driver.
It is another object of the invention to provide such an eye tracking system that permits nearly 180° head rotation, while continuing to monitor an eye.
It is yet a further object of the invention to provide such an eye tracking system that includes automatic driver identification.
It is yet an additional object of the invention to eliminate or greatly reduce the potential for “lost” eye contact.
It is yet another object of the invention to provide such an eye tracking system that uses high resolution methods to examine the entire face of a driver and retrieve and ocular profile based on the identification of the driver or to prepare and store an ocular profile, using a high resolution image of an eye, if the driver is not recognized. Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.